On Wed, 18 Feb 2004 10:05:58 GMT, Active8
,invalid wrote:


Gee. I could have sworn Jim was hinting at the math approach.
Wouldn'tcha just love to predict that roll-off on paper and *then*
see it in real life? Starts with an "F", looks like a number,
sounds like a frog.

Fourier? I wouldn't trust it. Sounds French. :-

--

The BBC: Licensed at public expense to spread lies.

On Mon, 16 Feb 2004 11:53:11 +0000,
said...
On Sun, 15 Feb 2004 16:46:32 -0700, Jim Thompson
wrote:

On Sun, 15 Feb 2004 23:48:47 +0000, Paul Burridge
wrote:

What's the maximum multiplication factor it's practical and sensible
to attempt to achieve in one single stage of multiplication? (Say from
a 7Mhz square wave source with 5nS rise/fall times.)

You ought to be able to answer that yourself... what's the spectral
roll-off of a square wave ??

I suppose it boils down to how much signal is left in the mush as the
harmonics get higher and higher. Knew I shoulda held on to that
spectrum analyser I used to have. :-(
I suppose that's the proper answer though: get the rise/fall times as
small and possible, measure the specral output and pick a suitable
harmonic with enough energy in it to set it 'comfortably' above the
noise floor?

Gee. I could have sworn Jim was hinting at the math approach.
Wouldn'tcha just love to predict that roll-off on paper and *then*
see it in real life? Starts with an "F", looks like a number,
sounds like a frog.

--
Best Regards,
Mike

I think it boils down to something very practical:

If you want good spectral purity, then you need to bandpass filter the
output of the multiplier. It becomes a matter of how close and how large the
undesired spectral components are compared to the desired spectral
components. After that, you can consult your filter design charts to
determine how complex a filter will be required and whether it's physically
realizable.

As an example, a x4 multiplier stage will have a desired output at Fin x 4,
and close-in undesired products at Fin x 3 and Fin x 5. This means the
output bandpass filter has to be able to attenuate signals at +/-25% of the
center frequency sufficiently to meet the desired spectral purity. In
practice with simple single-ended multiplier designs, a x4 multiplier is
approaching the threshold of realizability for high purity applications
(40-60 dB purity). It is possible to make push-pull and push-push
multipliers that have better output purity, but these techniques are seldom
used.

Joe
W3JDR



"Jim Thompson" wrote in message
...
On Sun, 15 Feb 2004 23:48:47 +0000, Paul Burridge
wrote:

What's the maximum multiplication factor it's practical and sensible
to attempt to achieve in one single stage of multiplication? (Say from
a 7Mhz square wave source with 5nS rise/fall times.)

You ought to be able to answer that yourself... what's the spectral
roll-off of a square wave ??

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

On Sun, 15 Feb 2004 16:46:32 -0700, Jim Thompson
wrote:

On Sun, 15 Feb 2004 23:48:47 +0000, Paul Burridge
wrote:

What's the maximum multiplication factor it's practical and sensible
to attempt to achieve in one single stage of multiplication? (Say from
a 7Mhz square wave source with 5nS rise/fall times.)

You ought to be able to answer that yourself... what's the spectral
roll-off of a square wave ??

I suppose it boils down to how much signal is left in the mush as the
harmonics get higher and higher. Knew I shoulda held on to that
spectrum analyser I used to have. :-(
I suppose that's the proper answer though: get the rise/fall times as
small and possible, measure the specral output and pick a suitable
harmonic with enough energy in it to set it 'comfortably' above the
noise floor?
--

The BBC: Licensed at public expense to spread lies.

On Sun, 15 Feb 2004 23:48:47 +0000, Paul Burridge
wrote:

What's the maximum multiplication factor it's practical and sensible
to attempt to achieve in one single stage of multiplication? (Say from
a 7Mhz square wave source with 5nS rise/fall times.)

While you might be able to generate odd harmonics of a 1 kHz square
wave up to several hundred megahertz, there are two practical
problems.

First you would need some method to separate the wanted harmonic from
the unwanted.

For low multiplication factors in HF/VHF a series of bandpass LC
filters would be needed to attenuate the unwanted harmonics. For
higher frequencies some helical or cavity resonators may be needed.

One old method to separate nearby harmonics is to use a wave analyser.
The wanted harmonics is mixed down with a VFO to some fixed
intermediate frequency in which a fixed crystal filter is inserted
(bandwidth 0,5-50 kHz depending on application). The filtered and
amplified signal is then mixed back to the original frequency by the
same VFO. The absolute stability of the VFO does not matter very much,
since any drift is cancelled in the up-conversion. However, the
stability must be sufficient to keep the desired harmonics within the
IF filter bandwidth. This kind of tricks was once used to multiply
some high precision frequency standard to some odd (say 61th
harmonic).

The other problem with high multiplication factors is that the
amplitude of the higher harmonics is quite low, thus needing quite a
lot of amplification after filtering. However, the level of the
original harmonics was low compared also to the wide band thermal
(white) noise, thus, after amplification, the wide band thermal noise
level is also high, reducing the final signal to noise ratio and in
reception, cause reciprocal mixing programs.

Thus, it is better to use several multiplier stages with low
multiplication factors, since it easier to filter out the desired
harmonics after each multiplier. The gain distribution is also better,
thus the noise floor does not become uncomfortably close to the wanted
signal.

However, if some strange multiplication factor (such as the 17th) is
needed (in which case a series of multipliers can not be used), these
days it would be easier to use a PLL with a fixed digital divider.
Keep the VCO tuning range as small as possible, thus reducing the
MHz/V sensitivity and noise through the tuning line and use a large
loop bandwidth to clean the areas around the generated signal.

Paul OH3LWR

On Sun, 15 Feb 2004 23:48:47 +0000, Paul Burridge
wrote:

What's the maximum multiplication factor it's practical and sensible
to attempt to achieve in one single stage of multiplication? (Say from
a 7Mhz square wave source with 5nS rise/fall times.)

You ought to be able to answer that yourself... what's the spectral
roll-off of a square wave ??

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

On Sun, 15 Feb 2004 23:48:47 +0000, Paul Burridge
wrote:

What's the maximum multiplication factor it's practical and sensible
to attempt to achieve in one single stage of multiplication? (Say from
a 7Mhz square wave source with 5nS rise/fall times.)

While you might be able to generate odd harmonics of a 1 kHz square
wave up to several hundred megahertz, there are two practical
problems.

First you would need some method to separate the wanted harmonic from
the unwanted.

For low multiplication factors in HF/VHF a series of bandpass LC
filters would be needed to attenuate the unwanted harmonics. For
higher frequencies some helical or cavity resonators may be needed.

One old method to separate nearby harmonics is to use a wave analyser.
The wanted harmonics is mixed down with a VFO to some fixed
intermediate frequency in which a fixed crystal filter is inserted
(bandwidth 0,5-50 kHz depending on application). The filtered and
amplified signal is then mixed back to the original frequency by the
same VFO. The absolute stability of the VFO does not matter very much,
since any drift is cancelled in the up-conversion. However, the
stability must be sufficient to keep the desired harmonics within the
IF filter bandwidth. This kind of tricks was once used to multiply
some high precision frequency standard to some odd (say 61th
harmonic).

The other problem with high multiplication factors is that the
amplitude of the higher harmonics is quite low, thus needing quite a
lot of amplification after filtering. However, the level of the
original harmonics was low compared also to the wide band thermal
(white) noise, thus, after amplification, the wide band thermal noise
level is also high, reducing the final signal to noise ratio and in
reception, cause reciprocal mixing programs.

Thus, it is better to use several multiplier stages with low
multiplication factors, since it easier to filter out the desired
harmonics after each multiplier. The gain distribution is also better,
thus the noise floor does not become uncomfortably close to the wanted
signal.

However, if some strange multiplication factor (such as the 17th) is
needed (in which case a series of multipliers can not be used), these
days it would be easier to use a PLL with a fixed digital divider.
Keep the VCO tuning range as small as possible, thus reducing the
MHz/V sensitivity and noise through the tuning line and use a large
loop bandwidth to clean the areas around the generated signal.

Paul OH3LWR

In article , Paul Burridge
writes:

What's the maximum multiplication factor it's practical and sensible
to attempt to achieve in one single stage of multiplication? (Say from
a 7Mhz square wave source with 5nS rise/fall times.)

Paul, past state of the hardware art (past 60 years) indicates that
triplers are the practical maximum. Quintuplers have been done
but those are rare in described applications.

In 1955 I had hands-on experience with a septupler (7 x multiplier)
using a 2C39 and a cavity-tuned plate circuit at 1.8 GHz. That was
in a General Electric microwave radio relay terminal designed about
1950. Of nine terminals, two had to "QSY" to new crystal-controlled
microwave center frequencies for second-level contingency operation.
Difficult and fussy to do but was do-able...the crystal was also 7th
overtone in a vacuum tube oscillator but was followed by a buffer
stage feeding a tripler, another buffer, then the septupler which fed
another 2C39 as the pulse-modulated final for 12 W peak output at
1.8 GHz. [from memory and 35mm slides...big GE manual went to
recycle a long time ago] That's the only septupler application that
I am aware of...no doubt there are others, somewhere.

General Electric must have had some division/work-group with lots
of work in old frequency control methods. A local NTSC color sub-
carrier generator-regenerator made by GE had extensive use of
"locked oscillators" for frequency multiplication and division, but
mostly at frequencies lower than 7 MHz. Haven't come across any
practical hardware on locked oscillators except for two mentions in
older journals, trade papers. One of those used transistors as
active devices.

Doublers and quadruplers have been made using both diodes and
tube-or-transistor active devices. That's relatively easy with non-
square waveforms (distorted sinewaves); square waves have high
odd harmonic energy, low even harmonic energy.

Making practical, reproducible active multipliers in the home shop
is, practically, a trial-and-error process involving playing with cut-
off bias of the active device input, energy and harmonic content of
the source, and Q of the multiplier's output stage. In the past I've
made tripling-in-the-plate pentode crystal oscillators using
fundamental frequency quartz but those were highly dependent on
getting the highest impedance tuned plate circuit and needed
scope viewing to check output waveforms. Not very reproducible.
There's no "easy" way to do it that will "work every time" despite
the claims of many. :-)

Digital division IS straightforward up to about 1 GHz based on
such technology over the last 3 decades. That's why PLLs came
to prominence in frequency control techniques up to UHF.

Len Anderson
retired (from regular hours) electronic engineer person

Avery Fineman wrote:
. . .
Making practical, reproducible active multipliers in the home shop
is, practically, a trial-and-error process involving playing with cut-
off bias of the active device input, energy and harmonic content of
the source, and Q of the multiplier's output stage. In the past I've
made tripling-in-the-plate pentode crystal oscillators using
fundamental frequency quartz but those were highly dependent on
getting the highest impedance tuned plate circuit and needed
scope viewing to check output waveforms. Not very reproducible.
There's no "easy" way to do it that will "work every time" despite
the claims of many. :-)
. . .

While that's certainly true of multipliers in general, I've certainly
found it very easy to make repeatable doublers with a two transistor
push-push stage. Driving it with about zero bias and a large enough
signal to get it to conduct on at least a good fraction of each cycle
gives plenty of harmonic energy. A collector circuit with decent Q will
take care of most higher harmonics, although a simple filter following
the stage is usually adequate for more demanding applications. The
fundamental can be nulled out reasonably well with a pot between
emitters with a grounded center tap. I'd think a push-pull tripler would
be nearly as easy, but I haven't had occasion to make one.

Several simple diode and transistor multipliers are described in Chapter
5 of _Experimental Methods in RF Design_, which I heartily recommend for
the homebrewer and experimenter.

Roy Lewallen, W7EL

In article , Roy Lewallen
writes:

Avery Fineman wrote:
. . .
Making practical, reproducible active multipliers in the home shop
is, practically, a trial-and-error process involving playing with cut-
off bias of the active device input, energy and harmonic content of
the source, and Q of the multiplier's output stage. In the past I've
made tripling-in-the-plate pentode crystal oscillators using
fundamental frequency quartz but those were highly dependent on
getting the highest impedance tuned plate circuit and needed
scope viewing to check output waveforms. Not very reproducible.
There's no "easy" way to do it that will "work every time" despite
the claims of many. :-)
. . .

While that's certainly true of multipliers in general, I've certainly
found it very easy to make repeatable doublers with a two transistor
push-push stage. Driving it with about zero bias and a large enough
signal to get it to conduct on at least a good fraction of each cycle
gives plenty of harmonic energy. A collector circuit with decent Q will
take care of most higher harmonics, although a simple filter following
the stage is usually adequate for more demanding applications. The
fundamental can be nulled out reasonably well with a pot between
emitters with a grounded center tap. I'd think a push-pull tripler would
be nearly as easy, but I haven't had occasion to make one.

Okay. I can't agree that they are "easy" after having enough
occasions to make several. :-)

Your mileage, of course, varies.

Several simple diode and transistor multipliers are described in Chapter
5 of _Experimental Methods in RF Design_, which I heartily recommend for
the homebrewer and experimenter.

A diode doubler using a toroid transformer, pair of diodes and a tuned
circuit in the output works fine right off the paper pad and slide-rule (or
calculator) numbers. Typically the source is a distorted sinewave
from either another multiplier or an oscillator. Rocket science it ain't.

BREADBOARD. A most handy part of the bench tools. Recommended
first. Especially for those purist hobbyists who think that digital
circuits
aren't "real radio." :-)

Playing with bias on a transistor multiplier stage is fine for optimizing a
multiplication but all it is is play when there's nothing to compare one
bias setting with another as to power output at the desired multiple.
A spectrum analyzer isn't an absolute need, by the way, there's other
ways to measure the harmonic content. Is that in "Experimental
Methods..." published by the ARRL? [I'm pushing work-on-the-bench,
not books, pardon my attitude that has resulted from years of having
to produce hardware results, not paper reports]

Len Anderson
retired (from regular hours) electronic engineering person